Effects Of Low Potassium Stress On Soybean Physiological Metabolism And Root Senescence

Four representative soybean varieties Tiefeng 36(low potassium tolerant soybean),Tiefeng 40(low potassium tolerant soybean),WM(low potassium tolerant soybean)and GD8521(low potassium sensitive soybean)were grown in 2015-2016 with hydroponic experiment and field experiment to study the difference of dry matter accumulation,nutrient absorption,osmotic adjustment substances,light photosynthetic characteristics,organic acid secretion and metabolism,ultrastructure and yield under low potassium stress.The study identifies the effects on physiological and biochemical mechanism and the relationship to root senescence under low potassium stress.It provides a theoretical basis for molecular breeding of low potassium tolerant soybean.The main findings were as follows.1.The soybean total root length,root volume and root average diameter were less than HK treatment under low potassium treatment,while the root surface area was larger than that.It suggested that low potassium stress promoted the transverse distribution of the root system in a certain extent,but a smaller role in the vertical.Low potassium tolerant soybean had a higher and more stable root surface area and root volume to ensure sufficient nutrient absorption from the soil,to promote plant growth,thereby to delay the senescence of plants under low potassium stress.2.Low potassium stress reduced plant biomass.In low potassium environment,low potassium tolerant soybean had a more stable dry matter accumulation in different growth periods.The ratio of GD8521 root had a higher change in different growth periods,and decreased greatly in mature period trend was caused by the root of premature aging.Low potassium tolerant soybean has a more stable root shoot ratio to adapt to the change of soil potassium in the plant,ensuring their growth and development,so as to achieve the effect of delaying the senescence of root.3.Low potassium stress reduced the nitrogen,phosphorus,potassium accumulation amount of soybean plant.Low potassium tolerant soybean can maintain more stable nutrient absorption material cycle and energy transformation for plant growth to postpone the senescence of plants and root in low potassium stress environment.4.Low potassium stress reduced the soybean leaves transpiration rate,the net photosynthetic rate and stomata conductance,leaded to increased inter-cellular CO2 concentration.Low potassium treatment increased the light compensation point of soybean,reduced the light saturation point and photo synthetic rate,which GD8521 light saturation point decreased 19.64%,T40 decreased 12.57%.Low potassium tolerant soybean can maintain CO2 concentration,the inter-cellular transpiration rate,net photosynthetic rate,stomata conductance,the light compensation point and the light saturation point in low potassium stress to prolong the functional period of the leaves,guarantee the supply of energy plants.It had made certain contribution for delaying the senescence of plants.5.The soluble sugar content of soybeans roots decreased and the proline and free amino acids content increased under low-potassium stress.The free amino acids content of T40 and WM roots reduced by 54.67%and 48.94%compared with HK treatment in 90 days after emergence,which GD8521 was 41.02%.The potassium tolerant soybean had low soluble sugar content and high free amino acids content in low potassium environment to maintain cell turgor to osmotic adjustment.6.The organic acid content of GD8521 were not significantly different in different K concentrations,while the low potassium tolerant soybean to maintain metabolic activity to maintain strong and material exchanges outside by the self regulation of the organic acid content in different K concentration conditions,thereby delaying the senescence of root.7.Low potassium tolerant soybean can remain stable cell structure in low potassium environment,had stronger chloroplast stroma and grana lamellae arranged orderly.There were more mitochondria around the chloroplasts,mitochondria membrane and cristae.It has stable cell structure that can maintain the normal function,effectively prolong the functional period of leaf photosynthesis,ensuring the healthy and orderly to make contribution to the root senescence.8.The yield of T40 and WM had a smaller change range than GD8521,which T40,WM and GD8521 reduced by 37.06%,46.34%and 64.77%compared with HK treatment.The results showed that low potassium tolerant soybean can maintain stable yield traits through auto regulation,and had the stronger ability to adapt to low potassium environment.